While ideally this is the situation, it really depends on the group of players. Nothing in the rules dictates that there cant be communication between the two or three teammates. If this were the case, I feel the allies would have a huge disadvantage, as, unlike the Axis, coordination is CRUCIAL between the allies, especially UK and UK. This is especially true when some players are more experienced than others. People are still free to disagree about moves, as US may not want to sacrifice their FTR or fleet in order to help out the Brits. But unless there is an agreement beforehand, I think that table talk is ok. One player dominating another player, however, should be avoided.
And besides, this is supposed to be a friendly, social game. And there was plenty of communication between the Allied leaders during the war, less so between Germany and Jap.
Of course when I lose a game, Everything my opponents did is wrong, whether it was table talk, serving me too many beers, or breathing too loud. But I have to admit, I can be a sore loser.
Mateooo